Evaluating New Copy-Prevention Techniques for Audio CDs J. Alex Halderman Princeton University Department of Computer Science

2 Copy-Resistant CDs - Overview Modified discs –Play on CD players, hard to read on PCs Response to “consumer piracy” Deliberate errors –Audio data / metadata Variations from several vendors Few discs today; many coming soon –BMG, EMI, etc.

3 Notable Drawbacks Primarily affects legitimate CD owners Confusing hardware/software errors Violates standards, bad engineering practice Effectiveness for reducing unlawful copying hasn’t been demonstrated

4 Interesting Questions for C.S. 1.Are they effective? 2.How do they work? 3.Can they be defeated? Who wants to know? Record companies, musicians, policy makers, software authors, music buyers, researchers

5 Music City, 2001 MediaCloQ (SunnComm) Tested Three Discs Columbia/Sony, 2002 key2audio (Sony) Universal, 2001 Cactus Data Shield (Midbar)

6 Not Addressed Why would anyone want to copy these discs?

7 Question 1 Are these techniques effective?

8 Test Configurations Covered range of deployed systems Operating System –Windows, Linux Hardware –Toshiba, Hitachi, IBM, Plextor drives Software –CD Player, MusicMatch, Nero, CloneCD (Windows) –CDP, CD Paranoia, CDR-DAO (Linux)

9 Test Results OSDriveSoftwareResult Win 98Toshiba*0/9 Win 2000 Hitachi IBM Sony CD Player MusicMatch Nero 0/9 CloneCD6/9 PlextorCD Player MusicMatch Nero 0/3 CloneCD3/3 LinuxHitachiCDP CDR-DAO 0/3 CD Paranoia1/3 PlextorCDP CDR-DAO 0/3 CD Paranoia3/3 Variety of errors –disc not detected invalid data crashes –Toshiba drive broken until reboot Most tests failed (62/75) Some successful –CD Paranoia, CloneCD (Plextor hardware)

10 Implications Seemingly effective today against deployed hardware, typical applications Some configurations already can play –Greater compatibility is possible Different modes of failure – Schemes use slightly different measures (more detail later)

11 Question 2 How do these techniques work?

12 How Do These Schemes Work? Exploit bugs, lack of robustness in hardware and software –Unexpected deviations from standards Two levels of failure –Hardware: Drives reject the discs (firmware) –Software: Apps fail even on “working” drives

13 Normal CD Structure Discs divided into tracks Tracks listed in table of contents (TOC) May be grouped into sessions Drives read TOC from each session, return list of tracks CD players only see session 1 Observed two main categories of deviations TOC Track 1 Track 2 … TOC Track … Session 1 Session 2 … CD players CD drives

14 Fake TOC Entries - Software Invalid TOC entries in session 2 –Bad track locations –Audio marked as data Drive returns invalid listing, fools software CD players only read first session, unaffected Real TOC Track 1 Track 2 … Fake TOC Session 1 Session 2 CD players CD drives Data Track

15 Fake Session Pointers - Hardware Session 2 contains pointer to fake session near outer edge of disk –Incomplete TOC, no lead out –Fatal errors in some hardware (e.g. Toshiba) Possible variations –No pointers to earlier sessions –Physical incompatibilities making earlier session hard to reach Real TOC Track 1 Track 2 … Fake TOC Session 1 Session 2 CD players CD drives Fake Session

16 Question 3 Can these techniques be defeated?

17 Felt-Tipped Pen Hack Hides last TOC containing invalid track/ session entries Drives see only first TOC, so disc can be read normally Outlaw felt-tipped pens! Last TOC area obscured by marker (Appeared on Chip.de early May 2002)

18 How to Adapt Hardware Direct fix — “compatibility mode” –Emulates CD player –Not even necessary Indirect fix — greater robustness –Fix bugs (firmware) –Better error reporting –More robust failure modes –Error interpolation

19 How to Adapt Software Bug fixes, greater robustness –Ignore obvious errors (warnings, not failure) –Scan for track starts by binary search –Interpolate over missing samples Changes ensure maximum compatibility with all faulty discs, not just copy-protected

20 Change is Underway Software –Audiograbber, CloneCD, and EAC have modes for handling protected discs Hardware –Plextor, others work today

21 Can They Be Defeated? Yes! –Offer minimal protection today, but will be easily adapted to (already happening) –Rate of adaptation proportional to rate of deployment –Schemes ineffective against copying in the near future (by the time they are widespread)

22 Conclusions Partial incompatibility with spec. won’t work –Software too easy to adapt and distribute Takes advantage of HW/SW flaws –Prohibiting circumvention would be to mandate bugs! Relies on stopping reading in most cases – but can be copied online if just some can read –True for tested discs –Circumvention easy, can’t be stopped everywhere

23 Conclusions In present form, these schemes are worse than useless –“Bad hacks” –Won’t prevent illegal copying –Inconveniences legitimate music owners –May make people less willing to buy CDs –Further alienates public from music industry Industry must find an alternative –DRM? New business model?